The invention relates to an X-ray having a rotary anode which is rotatably supported in a vacuum-tight housing by at least one metal-lubricated sliding bearing of which at least the cooperating bearing surfaces consist of a W-alloy and in which the lubricant is Ga or a Ga-alloy.
An X-ray tube of this type is particularly suitable as a source of radiation in medical diagnostic applications.
U.S. Pat. No. 4,210,371 describes such an X-ray tube in which a lubricant is used which consists of Ga and which furthermore, not counting impurities, may comprise In and/or Sn, which lubricant effectively wets the bearing surfaces. "Effective wetting" means that there is a wetting contact in which there exists a direct interaction between the metal atoms of the bearing surfaces and the atoms of the Ga or of the Ga-alloy, that is to say without an intermediate layer of, for eample, an oxide. The bearing surfaces preferably consist of W or Mo or of an alloy of W and Mo. Mo is preferably used because this can be machined more easily than W, due to the brittleness of W. When Mo is used the problem occurs that when the operating temperature of the bearing of the X-ray tube is above 400.degree. C. the bearing surfaces are attacked by the lubricant in which in particular the Ga present in aggressive and, for example, can form alloys with Mo. As a result of the formation of intermetallic compounds on the interface of the bearing surfaces and the lubricants the bearing may become clogged, which adversely influences the life of the X-ray tube.